Cyclohexyl chloride 3-elimination

The pyrolysis of (say) cyclohexyl chloride by the uni-molecular mechanism must involve. vvn-elimination (16 - 17) because the product is a cw-olefin. When I came across the pyrolysis of steroidal esters8,9 for the synthesis of olefins it seemed to me that sy/t-elimination (unimolecular mechanism)... 

These two diastereoisomeric cyclohexyl chlorides derived from menthol react very differently under the same conditions with sodium ethoxide as base. Both eliminate HC1 but diastereoisomer A reacts rapidly to give a mixture of products, while diastereoisomer B (which differs only in the configuration of the carbon atom bearing chlorine) gives a single alkene product but very much more slowly. We can safely exclude El as a mechanism because the same cation would be formed from both diastereoisomers, and this would mean the ratio of products (though not necssarily the rate) would be the same for both. 

Support for the c/j-nature of the elimination reaction has come from the work of Barton et on the pyrolysis of menthyl chloride, and the results of this study have recently been confirmed by Bamkole > who also examined the pyrolysis of neomenthyl chloride. The product ratio of menthene-3 to methene-2 is 3 1 in the case of menthyl chloride and 1 6 in the case of neomenthyl chloride, thus demonstrating a preference for m-elimination in each case. These two decompositions do, however, have some unusual characteristics the Arrhenius parameters are considerably lower than those reported for other secondary chlorides, and the rate of elimination of hydrogen chloride from each compound is appreciably faster than from cyclohexyl chloride . (The relative rate of pyrolysis of menthyl chloride and cyclohexyl chloride at 300 °C is about fifty.)... 

Because of the harsh conditions and high basicity of fluoride anions, these reactions are often accompanied by base-induced y3-elimination and decomposition of the TAA catalyst via the Hoffmann-type degradation. Particularly, secondary alkyl halides, cyclohexyl chloride, and 2-octyl bromide, in the reaction with KF under these conditions undergo -elimination. 

Typically, the organic substrate in these reactions is a haloalkane. Primary haloalkanes will generally give 100% substitution products, but tertiary and cyclohexyl halides usually undergo 100 % elimination, with secondary haloalkanes producing a mixture of the two. Studies of the chloride and bromide displacements of (R)-2-octyl methanesulfonate have shown that phase transfer displacements proceed with almost complete inversion of stereochemistry at the carbon centre, indicating an Sjv2-like mechanistic pathway [41],... 

The elimination of C1F from a scries of compounds RCH(OH)CCl2CF3 using the system aluminum (1.2 equiv) and lead(II) bromide (O.lequiv) with R = phenyl, 4-methoxyphenyl, 1-mesylindol-3-yl, cyclohexyl or zinc/aluminum(III) chloride with R = CHMePh, phenyl, 3,4-di-chlorophenyl, 1-phenylethyl, cyclohexyl has been described.180181... 

The unsubstituted hydrazones derived from aromatic ketones and aldehydes are converted to the corresponding alkyl chlorides, in high yield, under Swern oxidation conditions. In this unusual oxidation/reduction sequence, the substrate undergoes a net reduction. Unsubstituted hydrazones derived from cyclohexyl ketones yielded elimination products. The mechanism in Scheme 7 has been postulated.111... 

The same products, but in different ratios, occur in the gas phase eliminations of HCl from bornyl and isobornyl chlorides and from the pyrolysis reaction of bornyl and isobornyl benzoates and methyl xanthates . The isobornyl reaction is appreciably faster than that of the bornyl ester ((iso-B/B) = 6.8 at 345 °C), but proceeds at a slightly slower rate than that of cyclohexyl acetate, (CH/iso-B) = 2.1 at 600 °K. By analogy with the nonclassical carbonium ion interpretation of the solvolysis rates of bornyl and isobornyl chlorides, the participation of nonclassical carbonium ion intimate ion-pairs, e.g. 

Oxidation. Oxidation of alkyl halides by DMSO requires high temperatures (100-150°), and yields are relatively low except for primary iodides (1, 303). Epstein and Ollinger11 find that halides can be oxidized to carbonyl compounds by DMSO at room temperature (4-48 hours) in the presence of silver perchlorate as assisting agent. Chlorides are relatively unreactive, but bromides and iodides are oxidized relatively easily. Yields are higher with primary halides than with secondary halides. Cyclohexyl halides are oxidized to only a slight extent to cyclohexanone, the main product being cyclohexene, formed by elimination. 

Naked cyanide ion. Alkyl halides are converted into nitriles by potassium cyanide in the presence of a catalytic amount of 18-crown-6. Acetonitrile (or benzene) is used as solvent, and the two-phase system is stirred vigorously at 25-83°. Little or no reaction occurs in the absence of the crown ether, an indication that the ether is functioning also as a phase-transfer catalyst. Primary halides are also converted quantitatively into nitriles chlorides react much faster than bromides. A few percent of elimination products are formed in the reaction of secondary halides. Cyclohexyl halides give only cyclohexene by elimination. o-Dichlorobenzene fails to react. Methacrylonitrile undergoes hydrocyanation to 1,2-dicyanopropane (92% yield). 

The use of a flexible substituent (cyclohexyl) has presumably a beneficial role in the reductive-elimination step of the catalytic cycle by increasing the steric pressure on the metal center. Most aryl chlorides including sterically demanding ones can be converted to the corresponding biaryls at room temperature using this flexible ancillary ligand (see Fig. 5) [46]. 

A slight excess of 2-dimethylaminoethyl chloride added to a soln. of Na-1-phenylcyclohexoxide in toluene, and refluxed 1-3 hrs. with stirring 1-phenyl-cyclohexyl 2-dimethylaminoethyl ether. Y 75%.—y-, and d-Halogenamines give aminoethers whereas prim, alkyl halides form ethylene derivatives with elimination of hydrogen halide under the above conditions. F. e. s. B. Tchoubar and M. Verrier, Bl. 1960, 2151. 

The new zirconium hydride-alkyls, CpaZr(H)R, have been obtained by reduction of corresponding chlorides. They eliminate RH (R=cyclohexylmethyl, cyclohexyl, ethyl, octyl, or neopentyl) under hydrogenation in a reaction which has been demonstrated by labelling studies to involve initial co-ordination of dihydrogen (Scheme The starting chlorides react with CO rapidly at 0 °C... 

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